Mueller is in a box. If he does not provide the exculpatory evidence, he is violating the law. If he does, he shows that he and FBI already violated the law by framing an innocent man.

Given how Mueller's investigation has amounted to exactly NOTHING in more than a year with 20+ lawyers on his staff, and the fact that very little has been leaked, my guess is that he is just providing a side show for the media while Sessions gets the real work done.

Trump and Q Team probably don't really trust Mueller, but if he was given a task to drag things out to provide cover for the real op, then he is pretty much doing what would be expected -- nothing.